Generally, the mirror polishing of semiconductor wafers such as a silicon wafer etc., lenses, and glass substrates includes rough polishing primarily intended to regulate planarity and in-plane uniformity and final polishing primarily intended to improve surface roughness and removal of scratches.
The final polishing is carried out usually by rubbing a wafer against an artificial suede made of flexible urethane foam stuck to a rotatable platen and simultaneously feeding thereon an abrasive containing a colloidal silica in an alkali-based aqueous solution (Patent Literature 1).
As the polishing pad for finishing used in final polishing, the following polishing pads have been proposed besides those described above.
A suede finishing polishing pad comprising a nap layer having a large number of long and thin holes (naps) formed with a foaming agent in the thickness direction, in polyurethane resin, and a foundation cloth for reinforcing the nap layer is proposed (Patent Literature 2).
In addition, a polishing cloth having a surface layer having a thickness of 0.2 to 2.0 mm and an elastic compressibility of 50 to 4%, an intermediate support layer laminated on the back side of the surface layer, and having a thickness of 0.2 to 2 mm and an elastic compressibility of 2 to 0.1%, and a back layer laminated on the back side of the intermediate support layer, and having a thickness of 0.15 to 2.0 mm and an elastic compressibility of 50 to 4%, is proposed (Patent Literature 3).
A suede abrasive cloth for final polishing, in which surface roughness is expressed as an arithmetic average roughness (Ra) of 5 μm or less, is proposed (Patent Literature 4).
An abrasive cloth for final polishing, which is provided with a base material part and a surface layer (nap layer) formed on the base material part, wherein a polyvinyl halide or vinyl halide copolymer is contained in the surface layer, is proposed (Patent Literature 5).
In addition, a polishing fabric obtained by impregnating a substrate with a resin solution and then heating and drying the substrate is proposed (Patent Literature 6).
In addition, a polishing fabric obtained by coating a resin solution containing a polyvinyl halide or a vinyl halide copolymer on a substrate, subjecting the substrate to wet coagulation and then heat-treating the substrate is proposed (Patent Literature 7).
Conventional polishing pads have been produced by a wet curing method. The wet curing method is a method wherein an urethane resin solution obtained by dissolving urethane resin in a water-soluble organic solvent such as dimethylformamide is applied onto a base material, then wet-solidified by treatment in water, to form a porous grain side layer, which is then washed with water and dried, followed by polishing of the grain side layer to form a surface layer (nap layer). In Patent Literature 8, for example, an abrasive cloth for finishing, having roughly spherical holes having an average particle diameter of 1 to 30 μm, is produced by the wet curing method.
However, a conventional polishing pad had problems that durability is poor and the planarizing characteristics gradually deteriorates since the pad has a structure having elongated cells, or a mechanical strength of a material itself of a surface layer is low. In addition, there was a problem that, in the conventional polishing pad, a polishing rate is stabilized with difficulty.    Patent Literature 1: JP-A 2003-37089    Patent Literature 2: JP-A 2003-100681    Patent Literature 3: JP-A 2002-307293    Patent Literature 4: JP-A 2004-291155    Patent Literature 5: JP-A 2004-335713    Patent Literature 6: JP-A 2005-330621    Patent Literature 7: JP-A 2006-255828    Patent Literature 8: JP-A 2006-75914